1. Field of the Invention
This invention relates to start actuators for power tools such as power wrenches.
2. Description of Related Art
Hand-held powered assembly tools (e.g., straight, angle, crowfoot, open end, and/or pistol-grip power wrenches), typically include a motor (e.g., an electric or fluid-driven motor), an output drive connected to the motor via a drive train, and a manually operated start switch to initiate operation of the tool. The output drive (e.g., a socket or a square drive spindle adapted to engage a socket) is shaped to engage a further output drive (e.g., a socket) or a fastener to be tightened or loosened (e.g., nuts, bolts, screws, etc.).
Certain power tools can be so configured that there exists an operator hazard should the operator inadvertently place his hands near a potential pinch point. Several types of tool configurations present such hazards which, if guarded, would prevent the tool from being used for its intended purpose. One example of such a tool is an open-end wrench as described in U.S. Pat. No. 4,064,772. See also U.S. Pat. Nos. 3,257,877, 3,535,960, 3,636,698, 3,987,692, and 6,559,613. Open-end wrenches (sometimes referred to as tubenut wrenches) have a radially-extending opening in their housing through which a fastener may extend. The rotatable output drive also has a radially extending opening. When the openings in the housing and output drive are aligned, a fastener may be inserted through the openings into engagement with the output drive. As the output drive rotates within its housing to tighten or loosen the fastener, a pinch point is created as the opening in the output drive moves past the opening in the housing. Unfortunately, positioning a guard in the vicinity of the output drive might interfere with the tool's ability to reach the fastener to be tightened.
Tools that present such pinch points or other hazards are typically equipped with start actuators that require two separate motions to move to the start position. Such multi-step start actuators reduce the likelihood of unintentionally starting the tool, but do not prevent an operator's free second hand from coming in contact with a pinch point or hazard.
Tools can be equipped with dual start actuators that include a start actuator for each of the operator's hands. The two actuators are connected in series such that both actuators must be actuated in order for the tool to operate, thereby reducing the likelihood that the operator's hands are within reach of a pinch point or hazard. However, the restrictive positioning and inconvenient actuation of the secondary actuator typically hinders the normal operation of the tool as it is manipulated into position onto fasteners in a variety of positions. In such cases an operator may choose to defeat the intended safety function of the secondary start actuator by mechanically restraining it in its ON position.
In addition, when a secondary start actuator is positioned at a preferred location on the body of the tool, the physical size of typical commercially available electrical switches adds considerable size and weight to the hand-held assembly tool, placing an ergonomic burden on the operator. It is also often difficult and costly to route the electrical wires to the electrical switch associated with this secondary start actuator in a manner that prevents their damage when used in an industrial environment, thereby adding considerable cost and complicating any future maintenance of the tool.
In the machine control art, it is known to use “two-hand-no-tie-down” start actuators for stationary machines (e.g., metal punch presses) where the operator must use both hands to actuate two start actuators within a short time period of each other (e.g., ½ second) to start the cycle. Requiring both start actuators to be actuated within a short time period discourages an operator from mechanically fixing one start actuator into its ON position. The “two-hand-no-tie-down” system is used for stationary, floor mounted machines in which an operator's hands are not used to hold the machine or the work piece during operation. Accordingly, the dual start actuators are used to ensure that the operator's two otherwise idle hands are safely positioned.